mm: swap: unify cluster-based and vma-based swap readahead

This patch makes do_swap_page() not need to be aware of two different swap
readahead algorithms.  Just unify cluster-based and vma-based readahead
function call.

Change-Id: I45eeedb6347c245fbdb38744ac484119ade07d9c
Link: http://lkml.kernel.org/r/1509520520-32367-3-git-send-email-minchan@kernel.org
Link: http://lkml.kernel.org/r/20180220085249.151400-3-minchan@kernel.org


Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Git-commit: 9d1b4ad90ada396540a10ab5691671aa4c229a1d
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>